Horn Inheritance

“Horn Inheritance in Icelandic Sheep”
Written by Rebecca Alexander
First Published 06.19.2012
Revision 1 Published 12.31.2012.
Revision 2 Published 03.28.2015.
Revision 3 Published 12.06.2015.
Revision 4 Published 04.30.2017.

Horn inheritance occurs at the Ho locus in sheep. This locus has binding sites for two alleles (aka genes), and in Icelandic sheep, there are two different alleles that can bind to each site: the polled allele (P), and the horned allele (p’). In some literature, (p) is used to denote the horned gene as well, but I chose to use (p’) because (p) is also used in literature to refer to the sex-linked form of horn inheritance as found in breeds of sheep like Shetlands. Icelandics are not believed to have this form of inheritance, which results in horned males and hornless females in sheep that are homozygous (pp). Instead, in Icelandics, where two horn alleles (p’p’) are present, both males and females get horns. Where there are two copies of the polled allele, neither male nor female get horns.

It should be noted that in males, p’ is incompletely dominant to P, and in females, P is incompletely dominant to p’. What this means is that in a heterozygous (Pp’) male, it is more likely that he will express some form of horn or scur growth rather than expressing as fully polled. In a (Pp’) female, it is more likely that she will express as fully polled rather than displaying some form of horn growth. This subject will be addressed in more detail in the section below on heterozygous horned sheep.

For those unfamiliar with the terms: a phenotype is the visible expression of the allele. It is what you see; hidden (recessive) alleles are not taken into account. Compare this to genotype, which denotes the actual alleles present at the locus, despite what is seen. (A locus is simply the place on the DNA strand where particular alleles bind.)

An example: The Ho locus has two binding sites; P or p’ can each bind there. The options are: PP, Pp’, or p’p’, each representing a genotype. The phenotype, then, is what you actually see in each case. For example, the ewe I’ve used to show the phenotypic expression of being polled actually carries a hidden horn gene. So her phenotype is polled, and her genotype is Pp’.

The following is more about each horn combination, with pictorial examples of sheep showing the phenotypic expression of each:

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PP= no horns

An example of a ewe expressing as polled, with no horn growth at all. 10.23.2012.

Sheep that are homozygous polled often, but do not always, have indents where the horn buds would have been. Some still do have horn buds, and some rams will still grow little button scurs. These scurs are tiny and loosely attached, with no bony core. This means they are not attached to the skull, just to the soft tissues of the head. Such non-attached scurs are still generally registered as polled with the CLRC.

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p’p’= full horns

An example of the hornsets of three rams lambs, all with homozygous (p’p’) horns at about 6 months of growth. 10.10.2012.

Note how different the horns are on each ram in the example, despite all being about the same age. There seem to be other minor genes, often referred to as modifiers, at work that influence the shape and size of horns, that act in addition to the basic horn genotype of p’ and P. For example, if each of these rams is (p’p’), that means that each should grow full sized, symmetrical horns with heavy ridges. However, the different modifier genes at work account for some of the differences seen, such as the trajectory of growth pattern and overall horn length. More about these modifier genes later.

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Pp’= A wide range of expression.

Summary:
Where horn inheritance gets muddy is when the two alleles, horned (p’) and polled (P) are mixed, as this has a vast array of expression. (I usually call this heterozygous horned or heterozygous polled, depending on visible expression.) Horns are incompletely dominant in males, and polledness is incompletely dominant in females. What this breaks down to in males is that they usually have some form of horn expression, though it can range anywhere from tiny scurs to very full looking horns. (Though those full sized horns in a heterozygous horned male look a little different than in a homozygous horned male. They tend to be more round in cross section, and finer in build.) They can also get tiny horns, screwball little horns that grow odd directions, large scurs that tend to be brittle, and tiny scurs. Females tend to express as fully polled the majority of the time that they are heterozygous horned. They can also get scurs and small horns. I’ve yet to see a female with full sized horns carry a polled gene. It can make predictability quite difficult; is that ewe with no horns homozygous or heterozygous horned? Is that ram with the very full looking horns going to sire polled or scurred offspring, or is he fully horned? What is too bad is when an otherwise nice looking ram might have terrible growing horns due to being heterozygous horned, ones that will need constant cutting to keep them from pinching or growing into his head, thus either making him a high maintenance breeder or freezer bound. (Yes, this can still happen with homozygous horned sheep, but can also be mitigated with selective breeding- horn growth is largely genetic.)

The following is a break down by gender, to make it more understandable, and a list of each mode of phenotypic (visible) expression that I am currently aware of.

In females with Pp':

1. No horns at all; fully polled. Though a horn allele is present, there is no horn growth at all. This seems to be quite common for heterozygous horned females. I have encountered it often when studying CLRC pedigrees.

Cinthi and Solfi are twins, yet one has horns, the other, none. Solfi, on the left, carries one horned gene and one polled gene, but is expressing phenotypically as fully polled. She can still produce horned offspring. Taken the summer of 2012.

2. Small scurs. These are tiny little horn “buttons” that are barely visible, and loosely attached to the skull.

3. Large scurs. Irregularly shaped small horns that may or may not be asymmetrical.

4. Small horns. They look like full horns, but they are smaller or shorter than normal.

5. Full sized horns. I have never seen full horns in a heterozygous horned ewe, and it may not be possible.

In Males with Pp':

1. No horns at all; looks fully polled. This is more rare in males with a horn allele to not express any horns at all, but it does happen. AI Icelandic ram Langidalur, for example, has thrown horned offspring, though he himself is polled with no horn expression. (This gleaned from studying his pedigree in the CLRC.) This sometimes with a polled mother with no horned ancestry who was almost certainly homozygous polled. I have noticed from my studies of the pedigrees that most of the time, a ram that looks polled is homozygous polled.

2. Small scurs, or button scurs. Same expression as in females; little buttons of horn that are loosely attached to the head. Some may be a few inches long.

3. Large scurs. Similar to females, but larger. While I have not yet seen a case of a scurred females’ horns causing issue, larger scurs on a male can grow in any which way and are often asymmetrical. Some need to be cut to keep them from growing back into the head; some never cause problems. It seems to vary a lot individual to individual.

4. Small horns. These may or may not be asymmetrical; I’ve seen both. Sometimes one horn is just angled a little differently from the other; sometimes they are perfectly symmetrical and look like miniature versions of full horns. The problem with these is that a lot of times they grow too close to the face and have to be cut lest they gouge into the ram’s cheeks or eyes. If they grow too asymmetrically, the new path of a horn might make it grow into a place where it shouldn’t, like the neck. Again, phenotypic expression is highly variable ram to ram.

Freyr showing full horns, despite his ability to produce polled offspring.

Freyr (about 3 years old) and Ferdinand (about 1.5 years old.)  Freyr's horns are a little on the small side for his head.  12.31.2013.

Freyr (about 3 years old) and Ferdinand (about 1.5 years old.) Freyr’s horns are a little on the small side for his head. 12.31.2013.

5. Full horns. An example of this is my ram Freyr (pictured, large moorit spotted ram, later wethered). The horns are nearly indistinguishable from the smaller form of full homozygous horns. I have seen rams with smaller horns than Freyr’s with no polling in their ancestry, who must have had full homozygous horns. However, where the main difference lies is in the cross section. His horns are a bit more round than most homozygous horns, though not very much so. Most heterozygous horns express much rounder than this. A homozygous horned ram tends to have a more triangular cross section, to the point of being sunken in on the backside. The long angles on the horns are much more sharp in general too.

Chunk Monkey from the front.  08.12.2013.

Chunk Monkey is heterozygous horned. Note how his horns are smaller, smoother, more round in cross section, and demonstrate some asymmetry. 08.12.2013.

They also tend to express more smooth in texture; as in, those little cross ridges on the horns are less defined in a heterozygous horned ram. Chunk Monkey (black grey mouflon ram lamb, picture) illustrates this pretty well, especially when compared to his twin (also a black grey mouflon ram lamb, pictured.) You can see how his horns look more round and smooth in appearance than his brother’s. There is a photo of the two standing next to each other for further comparison. In general, the differences between heterozygous and homozygous horned rams is easiest to tell when they are still lambs. The ridges become more pronounced and the cross section becomes more triangular as the ram ages.

One more difference to look at is symmetry. Heterozygous horns are more likely to be asymmetrical. (Though some asymmetry can also be seen in homozygous horns.)

Big Flash posing.  09.06.2013.

Big Flash is homozygous horned. Note how much more angular and textured his horns are than his brother’s. 09.06.2013.

Big Flash and his twin Chunk Monkey, 60 days old.  A side by side comparison of their horns.  06.13.2013.

Big Flash and his twin Chunk Monkey, 60 days old. A side by side comparison of their horns. 06.13.2013.

It does appear appear that if a ram has double-spiral horns or horns with exceptional width from the cheeks, that they do have two horn alleles, though I have not seen enough cases of this to be certain.
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Personal notes: We at Waving Pines Farm ultimately switched to all horned stock, as it was one less thing to have to worry about when selecting breeding stock, was whether or not the sheep was fully horned or not. We like predictability on what traits that we can manage it. Plus, heterozygous horns are more likely to be problematic, growing to close or even into the head. We don’t need the extra management or maintenance.

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When it comes to horns, it seems that all the rules of inheritance that are set in place are put there purely to be broken, at least when it comes to phenotypic expression. The inheritance is simple: Each sheep gets one horn allele from each parent, of which there are two options: P or p’. But because of the incomplete dominance of P, the expression is vastly variable. I will continue to study this as time goes on and I can observe my own sheep, the sheep of others, and study inheritance in the CLRC pedigrees. This is my current knowledge based on these things. Expect to see this page updated as I learn more, and get more pictures!

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Other Aspects of Horn Inheritance Beyond Basic Alleles:

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Horn Narrowness and Closeness to the Face

Freyr’s horns were getting close, which is why he was wethered. There is about 1/2″ of clearance between the inside of his horn and his cheek. 11.18.2012.

I mentioned briefly before about the other minor genes that affect the end results seen in the horns of each sheep; the genes that act in addition to the base genes of P or p’. These genes, though poorly understood, are heritable. They are generally known as modifier genes, because they modify the phenotypic expression. Narrow or tight horns, as in, horns that grow close to the face on rams, have been shown to be heritable. Likewise, good horns often beget good horns. Two wide horned parents will typically produce good, workable wide horns in the lambs. I have seem farms with lines so predictably good that they will even offer a horn guarantee. Though as with most things genetic, it is not always so straight forward. Those modifier genes I mentioned seem to have a large enough effect to sometimes make predictability hard, especially in individuals bred at other farms where the genetics of the parents are not as well known as one’s own farm bred sheep. I will use my sire Ferdinand to help illustrate what I mean.

Ferdinand as a lamb had very heavy, wide-set horns.  09.15.2012.

Ferdinand as a lamb had very heavy, wide-set horns. 09.15.2012.

Note how wide those horns are; how much distance there is between each horn and his face. They look like they should be perfect. Fast forward about another year…

 

 

 

 

Ferdinand's second summer.  06.30.2013.

Ferdinand’s second summer. 06.30.2013.

Those horns still look great, though they have clearly swung closer to his face as compared to when he was a lamb. Especially note the angle of his horns in relation to his cheeks at the bottom of the curve. One more year later…

 

 

 

Ferdinand at two and a half years old.  Taken 09.01.2014.

Ferdinand at two and a half years old. Taken 09.01.2014.

Now those horns just look good; nothing special, but enough space is left between each horn and his face that they aren’t causing problems. In the end, that is the goal.

Ferdiand the end of his 4th summer.  10.31.2015

Ferdinand the end of his 4th summer. 10.31.2015

 

 

 

 

At the end of his fourth summer, Ferdinand’s horns have swung in enough that I needed to shave a little bit off of the inside of the right horn. The pattern of growth that his horns follow that cause them to swing in with age, coupled with the larger than average quantity of horn growth, have resulted in less than perfect horns at this age. At this point he was retired in favor of his son, TC, who has many of his father’s good traits, with better horns and better muscling in the rump and a better fleece. When paired with the right ewe, the pattern of growth that seems heritable from Ferdinand can result in excellent horns. That it can pass, however, is ultimately why he was retired.

Sting at about 6 months old.  10.15.2012.

Sting at about 6 months old. 10.15.2012.

An interesting side note to this is that Sting, who is the same age, still has decent horn clearance, though as a lamb his horns were much closer to his face than Ferdinand’s. Scroll down to the section on Sting to see a more detailed discussion on Sting. Sting’s pattern of growth for his horns which results in his horns following a consistent downward then outward track with little inward swing, coupled with a more average quantity of horn growth, has produced horns that have not been problematic. (Well, horn. The one horn that still grows normally. The skull fracture he sustained in a ram fight years back dramatically altered the horn trajectory of the damaged horn, which is obviously not genetic.)

However, what I have shown here has implications for heritability, as can be illustrated in his offspring. The first series is of Jack, a 2013 ram lamb born to Ferdinand and Freya. It shows his progression from a lamb up to a year and a half old, when he needed to be culled because his horns started touching his face.

Jack as a lamb, 60 days old.  06.18.2013.

Jack as a lamb, 60 days old. 06.18.2013.

As a young lamb, those horns swing out nicely.

 

 

 

Jack at 120 days old.  08.16.2013.

Jack at 120 days old. 08.16.2013.

 

 

 

Two months later, they have developed their distinct curve, which still looks pretty good. The angle is not too dissimilar from Ferdinand’s as a lamb.

 

 

 

Jack at 6 months old.  09.25.2013.

Jack at roughly 5 months old. 09.25.2013.

 

When Ferdinand and Jack are both compared at 5 months old, Jack’s horns have an almost identical set to them; they are just smaller overall with less growth. For his size, they are rather coarse.

 

 

 

Jack at about a year old.  05.15.2014.

Jack at about a year old. 05.15.2014.

 

By about a year old, Jack’s horns are looking distinctly troublesome.

 

 

 

Jack as a hogget, a bit over a year old.  July 4, 2014.

Jack as a hogget, a bit over a year old. July 4, 2014.

 

 

Getting into his second summer, at a little over a year old, Jack’s horns are curling back out from his face a bit. However, they are still too close for a ram his age, with two whole summers worth of growth left.

 

 

 

Jack at a year and a half old, taken 09.18.2014.

Jack at a year and a half old, taken 09.18.2014.

 

By a year and a half old, those horns, as suspected, touched into his face. He was culled shortly afterwards.

 

 

 

 

 

Note that they had the same basic growth pattern as Ferdinand: They swung out wide initially as a lamb, then curved back inward as they grew. The reason it became a problem in him that is that Jack’s horns did not have as much growth as Ferdinand’s. Ferdinand had so much horn growth when young that they had plenty of room still when his horns swung back towards his face. Jack’s horns did not put on so much growth, but still swung inward a similar degree. These are all observational data so far, but the same pattern repeated in the same crossing the next year. This is the Brick, a 2013 ram lamb by Freya and Ferdinand.

The Brick at 62 days old.  07.03.2014

The Brick at 62 days old. 07.03.2014

The Brick’s horns start out about the same as Jack’s, coming out of the head nice and wide.

 

 

The Brick from the front, right after shearing.  I love that square chest and leg set.  134 days old.  09.13.2014

The Brick from the front, right after shearing. I love that square chest and leg set. 134 days old. 09.13.2014

 

 

 

His horns are growing at a faster rate than Jack’s, though at this age have a similar growth pattern. (This may be genetic in Jack, or may be nutritional. The lambs of 2014 received more cobalt than the lambs of 2013, and thus performed much better.) They again bear a similar growth pattern to Ferdinand.

The Brick at almost a year old.  03.29.2015.

The Brick at almost a year old. 03.29.2015.

The Brick is very docile and easy to handle; he loves cheek, chin, and chest rubs.  You can see how his horns are turning out at this age here too.  Taken 07.14.2015

The Brick. Taken 07.14.2015

 

 

 

The Brick at almost a year old has much nicer looking horns than Jack did at about the same age. They distinctly swing out at this age rather than slightly in like Jack’s did. They are also almost identical to his father Ferdinand’s at the same age for growth pattern (see the above picture of Ferdinand at a little over a year old.) Though his growth rate was still not quite his father’s, it appears that he put on enough growth to get enough clearance.

By the end of his second summer, they are still maintaining nicely enough that I believe they will be okay. They do have less inward swing that his father as a whole. He was sold as a breeding ram.

 

 

 

 

 

 

These instances seem to illustrate that Ferdinand has at least one modifier gene that causes horns to start out wide and then swing back in rather dramatically with age. His is not the first case I have seen of a ram passing such a pattern onto his offspring. However, this is still not 100% heritable, as genes do come in pairs, and not all of Ferdinand’s offspring display this same pattern of horn growth. Take, for example, his son TC, out of Isadore.

TC at a little over a month old. 06.07.2014.

TC at a little over a month old. 06.07.2014.

TC at a little over a month old already looked different that Jack or Brick; his horns had a lot more loft upward than the other two, who’s horns came out almost horizontally.

ThunderCheeks (TC) at 126 days old.  Taken 09.06.2014.

ThunderCheeks (TC) at 126 days old. Taken 09.06.2014.

 

 

 

 

As a lamb, TC’s horns are finer and swinging out even wider than Jack or Brick’s horns. They also have more length overall. He is roughly four months old here.

Brick (left) and TC (right), as a horn comparison.  They are about 5 months old.  09.13.2014.

Brick (left) and TC (right), as a horn comparison. They are about 5 months old. 09.13.2014.

 

 

 

 

 

Here is a comparison of TC standing next to The Brick. It is easy to see just how much farther out TC’s horns are swinging.

Thundercheeks at almost a year old.  01.14.2015.

Thundercheeks at almost a year old. 01.14.2015.

 

 

 

 

 

TC’s horns have swung out much wider initially, and even now, while Brick’s horns are curling in towards his face, TC’s are maintaining their distance. They appear to be growing straight downward, with the curl beginning to go out without diving in at all.

 

 

TC, Aug. 20, 2015, almost 18 months old.

TC, Aug. 20, 2015, almost 18 months old.

At the end of his second summer, TC’s horns continue to look excellent. So maybe he did not get his father’s modifier that causes horns to swing inward, or maybe his mother’s modifier that tells horns to grow straight down rather than swinging towards the face overroad that gene, whether through complete or incomplete dominance (more later.) Maybe it’s whatever modifier tells the horns to have a greater loft; it does seem that horns that loft higher on the head, versus horns that are more level with head, are less likely to dive into the face later. He also has finer horns; in other words, less horn growth in both overall length and in width. I believe this too contributes to his nice horn set.

Isadore at about 2 and a half years old.  09.17.2014

Isadore at about 2 and a half years old. 09.17.2014

Another thing I noticed is that TC’s horns look almost identical to his grandfather Thunder’s horns at that age. (I have seen a photo of Thunder as a lamb, but do not own it to be able to post it.) I can post a picture of his mother, however. She has really nice wide horns.

 

 

 

What we see in the case of the Isadore and Ferdinand cross is two wide horned parents producing a wide horned offspring. As I mentioned previously, and have attempted to show in the photos above, modifiers can create less than predictable results. Here is a picture of Freya…

Freya with her lamb The Brick at 127 days old.  09.06.2014.

Freya with her lamb The Brick at 127 days old. 09.06.2014.

Note that Freya, who is pictured with her 2014 son, The Brick, has horns that swing out wide. However, they do have less loft than Isadore’s, and curl down more. More research is needed to see how this translates into ram horns.

 

 

 

What we see in the case of the cross of Freya and Ferdinand is what appears to be two wide horned parent producing narrow horned offspring. I will break this down into possibilities of heritability, with the understanding that genes always come in pairs. Thus, Ferdinand has two modifier genes within a set that affect horn growth pattern, and so does Freya. Ferdinand appears to have one modifier gene that codes for horns swinging in, but one that does not, since it is not 100% heritable for his offspring to have horns that swing in. Freya has very nice wide swept horns, but somehow her modifier genes allow for the growth pattern that causes horns to swing in. One possibility is that she has one modifier gene that causes horns to swing in, and one that cause horns to be more wide swept. The wide swept horn gene is dominant, and thus she displays wide horns. Under this theory, she could pass that good wide swept gene and produce wide horned offspring, though this has yet to be seen. Or maybe she has one gene for wide horns, one for horns that swing in, and they are incompletely dominant. Incomplete dominance tends to have a range of expression, and maybe in this case her wide swept horn gene has mostly dominated the other one, thus the expression of wide horns. This would explain how she could pass a tight horn gene though expressing wide. Applying the idea of incomplete dominance towards expression in the offspring, both genes, one given from each parent, would be able to express to varying degrees. The range could be anywhere from looking nearly completely like one parent to being an even split between the two. I do tend to lean towards the idea of incomplete dominance of genes as an explanation, for two reasons: One, base horn genes, as in those that code for either horned or polled, are incompletely dominant. Two, there is such a wide range of horn expression and such difficulty in predicting it that it seems too complex of an inheritance for just simple dominance. Speaking of which, another possibility is that she does have two modifier genes that both code for wide swept horns, but Ferdinand’s gene that causes horns to swing in could be dominant to it, whether completely or incompletely, and thus override it.

I will contribute one more example, this time of a narrow horned ewe (April) being crossed with Ferdinand. April’s mother had extremely narrow horns that pressed tightly against her skull. She almost exclusively threw tightly horned offspring, suggesting that she always contributed a modifier that caused horns to grow tightly to the face. Since genes always come in pairs, both modifier genes in this set appear to code for a tight horn growth pattern. (Granted, there may be multiple modifiers sets at work here, but for simplicity’s sake, I am only hypothesizing on those that I see.) April’s mother was paired with a wide horned ram, so theoretically April carries one gene for wide swept horns from her father.

April and her 2014 ram lamb.  05.23.2014

April and her 2014 ram lamb. 05.23.2014

She appears to have certainly gotten that very tight horn growth gene from her mother. It can be seen here how April’s horns swing way back, behind her head, and curl in close to her face.

 

 

 

April's ram lamb at 74 days old.  (About 10 weeks.)  07.03.2014.

April’s ram lamb at 74 days old. (About 10 weeks.) 07.03.2014.

 

Her 2014 son’s horns were tight from an early age. They are also sweeping way back, following the neck line behind the ears without much clearance from the face. This is evident at just over two months old.

 

 

14B right after shearing.  09.13.2014

14B right after shearing, about five months old. 09.13.2014

 

His horns were touching the back of his cheeks by 6 months old, when he was culled. It is uncertain whether or not he got Ferdinand’s gene that causes horns to swing in, as his horns were already so close to his face that he was culled before they had the chance to start swinging in.

 

 

 

Sting at about 6 months old.  10.15.2012.

Sting at about 6 months old. 10.15.2012.

Sting as a yearling. 11.01.2013.

Sting as a yearling. 11.01.2013.

Sting at about two and a half years old.  12.27.2014

Sting at about two and a half years old. 12.27.2014

Sting from the front, his 4th summer.  10.31.2015

Sting from the front, his 4th summer. 10.31.2015

I have focused quite a bit on the inconsistencies of the inheritance of the growth pattern of horn genes. Now I will include an example of a line of horns that are very consistent. Sting’s horns were not spectacularly wide set as a lamb; at a glance, I would call them good. I have seen lambs with wider hornsets than this. Though ironically, two of them are the Brick and Jack. Sting’s horns are also not all that coarse, and grow mostly straight down rather than inwards.

 

 

Still growing well his second summer.

 

 

 

 

 

 

In the next photo, only his right horn is to be counted towards his growth potential; he got into a bad fight the previous winter with another ram, resulting in a skull fracture that altered the growth trajectory of his left horn (among other things…) In other words, the cut left horn is growing weirdly because the base of the horn was crushed and healed wrong. But his right horn is alright.

These consistently growing horns after the completion of his fourth summer appear that they will never cause problems. His father was the same way, and tended to pass the same. As his breeder aimed for consistent horns, Sting’s mother also likely contributed such to Sting. He should only have these consistent horn growth modifier genes, and thus pass only them to his offspring. This will only be seen with time. The ewe also still contributes half of the influence on those horns.

Azalea the end of her second summer.  11.01.2015

Azalea the end of her second summer. 11.01.2015

Penny the end of her second summer.  11.02.2015

Penny the end of her second summer. 11.02.2015

Here are two examples of Sting’s daughters, who are related on the mother’s side too. Azalea is the daughter of Tryna, and Penny is from Tryna’s daughter Cinthi. Penny’s horns look the same as Tryna’s, which are also the same as Cinthi’s. Azalea’s look very different, which I speculate is primarily Sting’s influence based on what has often passed from the ewe side of this line. It will be interesting to see how a son of Sting’s horns turn out.

 

 

 

 

 

 

And for reference, their mothers:

Tryna.  Taken 05.12.2012.

Tryna. Taken 05.12.2012.

Cinthi shortly after shearing, as a yearling.  10.21.2013.

Cinthi shortly after shearing, as a yearling. 10.21.2013.

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Coarseness of Horns

Bane (left) has fine horns for a ram.  Ferdinand (right) has very coarse horns.  These two are about the same age.  Even if you ignore size difference, proportionally Ferdinand has much larger, coarser horns than Bane.  I would never use Ferdinand on a ewe lamb for fear the horn buds would be too large for her to pass.

Bane (left) has fine horns for a ram. Ferdinand (right) has very coarse horns. These two are about the same age. Even if you ignore size difference, proportionally Ferdinand has much larger, coarser horns than Bane. (Bane was later culled due to ill thrift.) 09.15.2012

Brick (left) and TC (right), as a horn comparison.  They are about 5 months old.  09.13.2014.

Brick (left) and TC (right), as a horn comparison. They are about 5 months old. Note how much heavier looking the Brick’s horns are as compared to TC. 09.13.2014.

The coarseness of a horn refers to how wide the horn is, as in, it’s thickness and diameter. Very thick, coarse horns are not considered desirable, the biggest reason being that they result in larger horn buds on the lambs. Large horn buds make for a more difficult birth for the ewe. It is the head on a ram lamb that has the hardest time coming out due to those horn buds. The bigger they, the more stretching is needed to pass them.

 

 

The second reason they are not desirable is more anecdotal, but it appears coarser horns also tend to have a tighter curl and a higher likelihood of swinging into the face. Plus, being thicker in and of itself makes the horns closer to the face than a finer horn. A two and a half inch wide horn is a half inch closer to the face than a two inch wide horn, for example. I will pull back Ferdinand and his 2014 sons, Brick and TC, as examples.

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Age of Ram, in Consideration

This is Freyr’s hornset as he turned a year old in the spring of 2011. I provide this for comparison to how his horns looked in the fall of 2012, at 2.5 years old. His horns look great here, but it seems his huge, wide forehead that developed as he aged outgrew his horns. Photo courtesy of Heartbreak Farm.

Freyr at about 2.5 years old.  11.18.2012.

Freyr at about 2.5 years old. 11.18.2012.

Another thing to keep in mind when determining how close a ram’s horns are is age. The major horn growth occurs within the first three years of a ram’s life. By the fourth summer, the horns are all but done growing. In the first picture of Freyr, he is just a yearling. The hornset actually doesn’t look too bad, with decent space between cheek and horn. However, because these are heterozygous horns, they do tend to grow to a smaller overall size. It makes these horns harder to predict than the other examples of yearlings I gave previously.

In the later picture of Freyr, he is about two and a half years old. If I’d left him as an intact ram, those horns very likely would have cut into his face if not cut. Wethering him removed the testosterone that drives horn growth and all but stopped it. Point being, what looks good as a lamb, and sometimes even as a yearling, will not necessarily stay good later in life. It is really hard to predict how a hornset will grow before a year old, since that is about when the horns start to display their growth pattern. Even then, knowing the history of horn growth in the family will be very helpful in making educated guesses. For example, will they start swinging in? Growing straight down? Even growing out? In relation to growth pattern, how thick are the horns? As the thicker base moves downward, will it be too wide to clear the cheek? What about head size? In Freyr’s case, his wide head seemed to outgrow his horn growth. Obversely, once a ram has made it past his third summer, on can be much more certain about the hornset.

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Nutrition

A diagram of Freyr's horn the spring of his second year, showing the difference in growth ring size between the seasons.

A diagram of Freyr’s horn the spring of his second year, showing the difference in growth ring size between the seasons.

Another factor, nutrition, is far less understood. What is known is that good nutrition will keep horns growing to their full potential. What is less known is how less than ideal nutrition can affect the tightness of the horns. I have observed during times of abundant nutrition, like in the spring on fresh grass, the horizontal ridges, or rings, of the horns grow wider than the rings in the winter when on hay. A specific example is Freyr. We had poor hay last winter, and he grew very tight rings. As soon as he got on pasture, they got much wider. Other rams I have seen, presumedly on better hay, had less tight rings, though still tighter than their summer rings. Of course, there may be seasonal effects at work too. Point being is that the amount of growth as it pertains to nutrition can play a role in how the horns will turn out. Just how much, I can’t say.

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Horn Color

Some examples from my flock of various horn colors.

While not really important, it is a fun point to mention, as horns do come in many different colors. The standard seems to be solid steel grey on moorit sheep or black on black sheep. Spotted sheep tend to have vertically striped pink and grey or black horns. Grey sheep tend to have horizontal bands of alternating pink and grey. Horns can also be all pink, usually in white sheep, though also in spotted. These are not absolute, only trends I’ve observed, and any of these mentioned can also still just have solid grey or black horns.

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Quantity of Horn Growth (Horn Size)

Freyr (about 3 years old) and Ferdinand (about 1.5 years old.)  Freyr's horns are a little on the small side for his head.  12.31.2013.

Freyr (about 3 years old) and Ferdinand (about 1.5 years old.) Freyr’s horns are a little on the small side for his head. 12.31.2013.

Ferdinand at two and a half years old, just a little younger than Freyr in the previous picture, but with proportionally larger horns.  Taken 09.01.2014.

Ferdinand at two and a half years old, a little younger than Freyr in the previous picture, but with proportionally larger horns. Taken 09.01.2014.

Sting has proportionally larger horns than Freyr at 2.5 years old.  12.06.2014.

Sting has proportionally larger horns than Freyr at 2.5 years old. 12.06.2014.

For this I am referring to the overall length of horn if you were able to unwind a horn to make it straight. Some sheep put on more overall growth than others; some rams have grand double spiral horns, others have a simple single curl. This too appears to be heritable, though how much affect it has on overall horn tightness is hard to say. It does seem that horns that grow more slowly and put on less growth overall have less time to get a good distance from the face that first year. How much this matters depends on how the angle of the horn growth and its growth pattern. If the horns swing in towards the face, much distance is needed that first lamb year in order to keep the horn from swinging back into the face. But if the horns grow straight down or even out, the amount or rate of growth do not matter.

The overall amount of growth can be an indicator of a heterozygous horned ram (like Freyr), which tends to put on less overall growth than a homozygous or fully horned ram. This must be taken into consideration with other factors, though, as fully horned rams can also have small horns without a lot of overall growth.

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Horn Shape

Here is a comparison of three different ewes with varying horns shapes: Freya (left) has wide set horns that angle out to the sides, with the tips curling out; Lilija (middle) has shorter horns that sweep back more, with the tips curling down; Tryna (right) has very long horns that angle back and down and curl into a C-shape.

This could arguably be considered a product of overall horn length, but I think there is enough variation, especially among ewes, for it to justify its own heading. Some ewe horns are more goat-like; short, straight, and come out mostly behind the head. Others are more elongate and come out the side of the head. And still others are more round in shape as they curve downward. I have included a few examples.

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Horn Cross Sectional Shape

The blue dotted line and arrows indicate the ridge I mention.

The blue dotted line and arrows indicate the ridge I mention.

Two 2103 ram lambs, Chunk Monkey (left) and Big Flash.  CM is heterozygous horned; BF is fully (homozygous) horned.  06.13.2013

Two 2103 ram lambs, Chunk Monkey (left) and Big Flash. CM is heterozygous horned; BF is fully (homozygous) horned. 06.13.2013

If you were to cut across a horn, what shape would the slice be? Primarily, this is triangular due to the large ridge at the back of the horn that runs most of the length of the horn. There is definitely a range in what type of triangle expresses. Some are flatter, some more angular and symmetrical. Horn cross sections can also be more round. If it is round to the degree of lacking any ridge at all in a ram as a lamb, there is a good chance that the ram is heterozygous horned. So this is partly an aesthetic trait, partly an indicator trait if the horn genotype is in question. I have included a picture of twin ram lambs, one of who is heterozygous horned, and the other of whom is homozygous horned.

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Symmetry

Freyr demonstrates what nice symmetrical horns look like, from the front and from above.

Freyr demonstrates what nice symmetrical horns look like, from the front and from above. He is heterozygous horned.

Stingson with Mr.Moufknutts, 03.27.2017

Stingson with Mr.Moufknutts, 03.27.2017. All pictured are homozygous horned. Mr. Moufknutts shows slightly asymmetrical horns.

When looked at from the front, do both horns come out of the head and spiral down at about the same angle? How close are they to being mirror images of each other? Again, this is partly an aesthetic trait, and partly an indicator of heterozygosity. It is possible for homozygous horns to be asymmetrical, but they usually aren’t. Likewise, heterozygous horns are often assymetrical, though not always. This is definitely a trait that must be considered with others when trying to figure heterozygosity.

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Conclusion

The point of mentioning these examples, other than to hopefully satisfy the curious mind, is to emphasize the importance of taking these things into account when making breeding decisions. Horns that grow into the face are a problem; they make chewing more difficult, as the jaw moves side to side to chew, and in more severe cases, they actually cause sores in the skin, which can lead to infection. Some opt to just cut them off, but personally I aim to breed them out of my lines. In Iceland they don’t pay as close of attention to horn shape because they don’t mind trimming horns as a regular maintenance. It is up to each breeder to decide the importance of this to his or her breeding program.

References:

Budde, Juliann. “The Polled Allele and Shetland Sheep.” http://www.shetlandsheepinfo.com/CONFORMATION/polled.htm

CLRC Electronic Herdbook. http://www.clrc.ca/cgi-bin/query.cgi?_association=30

Harker, Liz. “Horn Inheritance in Icelandic Sheep: An Interview with Emma Eythorsdottir” ISBONA Newsletter, Volume 5 No. 4 Fall 2001. Article linked here. http://www.isbona.com/images/pdf/newsletterarticles/horninheritance.pdf

Holcombe, Gary J. “Breeding Issues…Information for Better Choices, an interview with Gudmundur Johannesson.” Northern Maine Icelandics Website. Article linke here. http://www.northern-maine-icelandic-sheep.com/MundiInterveiw1.html

Kimball, Rich. “Horn Genetics Update.” ISBONA Newsletter Volume 2, Number 1 January 1998. Link died.